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                集会                </h1>
                <p>时间限制：10s&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  空间限制：256MB</p>			</div>
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                                <h3>题目描述</h3><p><div>Fictitia是一个很大的城市，他的街道由许多横向和纵向的街道垂直交叉组成，每两条相邻的横向街道距离为1，每两条相邻的横向街道距离也为1。每个十字路口有一个整数坐标(x,y)。所有的市民都居住在某个十字路口。</div>
<div>有一天，Fictitia中有一群不高兴的市民准备集会。他们想选一个十字路口(x&rsquo;,y&rsquo;)作为集会地点，使得所有人离集会地点的曼哈顿距离的总和最小。如果某个市民居住在(x,y)，那么他与集会地点的曼哈顿距离为|x-x&rsquo;|+|y-y&rsquo;|。</div>
<div>但为了让所有人及时赶到，集会地点离每个市民的曼哈顿距离不能超过d。市民们想知道最小的距离总和为多少，如果不存在合理的集会地点，输出&ldquo;impossible&rdquo;。</div>
<p></p></p><hr/><h3>输入格式</h3><p><div>每个文件有多个输入数据，文件最后一行为一个数0。</div>
<div>对于每组输入数据</div>
<div>第一行为一个正整数n（n&gt;=2），表示集会市民的人数。</div>
<div>接下来的n行，每行两个整数x，y（0&lt;=x，y&lt;=10^9），表示每个市民居住地点的坐标。</div>
<div>最后一行一个整数d（0&lt;=d&lt;=2*10^9），表示集会地点与每个市民居住地点的最大距离。</div>
<p></p></p><hr/><h3>输出格式</h3><p><div>对于每个测试输入，如果存在合理地点，输出一行，包含一个整数为最小的距离总和；否则输出一行&ldquo;impossible&rdquo;。</div>
<div></div>
<p></p></p><hr/><h3>样例输入</h3><pre>5
3 1
4 1
5 9
2 6
5 3
10
5
3 1
4 1
5 9
2 6
5 3
5
5
3 1
4 1
5 9
2 6
5 3
4
0
</pre><hr/><h3>样例输出</h3><pre>18
20
impossible
</pre><hr/><h3>提示</h3><p><p class="MsoNormal" align="left"><span lang="EN-US">100%</span><span style="font-family:宋体;mso-ascii-font-family:Calibri;mso-hansi-font-family:Calibri">的数据，</span><span lang="EN-US">n&lt;=100000</span><span style="font-family:宋体;mso-ascii-font-family:
Calibri;mso-hansi-font-family:Calibri">，每个文件中所有数据</span><span lang="EN-US">n</span><span style="font-family:宋体;mso-ascii-font-family:Calibri;mso-hansi-font-family:Calibri">的总和不超过</span><span lang="EN-US">300000</span><span style="font-family:宋体;mso-ascii-font-family:Calibri;
mso-hansi-font-family:Calibri">；</span></p>
<p></p></p><hr/><h3>题目来源</h3><p>没有写明来源</p>
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